Microwave heating apparatus



Oct. 8, 1963 Filed Sept. 14, 1960 L. H. SCHALL MICROWAVE HEATINGAPPARATUS 2 Sheets-Sheet l V l l 23 el NVENTUR LOUIS H' SCU/ALL BWMMATTOHND" Ochs, 1963 L. H. scHALL 3,106,629 MICROWAVE HEATING APPARATUSFiled Sept. 14, 1960 2 Sheets-Sheet 2 ATTORNEY United States PatentOtilce 3,106,629 Patented Oct. 8, 1963 Ware Filed Sept. 14, 1960, Ser.No. 55,960 3 Claims. (Si. 219-1655) This invention relates generally toheating devices and more particularly to apparatus utilizing highfrequency energy for the heating of materials.

In orde-r to pro-vide uniform and rapid heating of materials, high`frequency energy, generally in the microwave region, may be utilized.The materials to be heated, which may be ioodstuifs, Vor Votherindustrial materials, are placed in an enclosure which is sealed 4toprevent the escape of the high frequency energy. The energy, which isgenerated by .a known high frequency energy source, such as a magnetron,.is inserted either directly into the enclosure or indirectly throughthe use of wave guides or other suitable devices.

ln order to provide the most ecient heating of the material, the energyis directed toward the material from a location above the material. Forthis reason the magnetron is generally located at the top of theenclosure. It is advantageous that the power supplies and otherelectr-ical or mechanical equipment utilized in the apparatus be locatedbelow the enclosure, or oven cavity. In conventional coniigurationsjwherein the magnetron is placed at the top of the oven and the powersupplies located below the enclosure, extensive cabling and relativelycomplicated construction design is required in order to transmit energytrom the power supply to the magnetron and thence into the oven.Alternatively, the magnetron may be placed below the roven cavity andthe energy inserted through the bottom of the oven enclosure in order toavoid these construction diiliculties. However, such a bottom-feeddevice prevents the uniform heating of the material since, as mentionedabove, it has been found that the best heating is obtained when theenergy is coupled into the oven at a point above the load lto be heated.In addition, for conventional bottom-feed construction, the magnetronmust be protected from damage due to vapors or spillage of liquids thatare being heated and, hence, extensive waterproong of Vthe bottomsection is required.

This invention combines the advantages of coupling the high frequencyenergy into the enclosure at a region located above the load to beheated and the advantages of locating the microwave energy source iat aposition below the enclosure, ywithout the normal disadvantages thatusually accompany each. In one particular embodiment of the invention,the enclosure comprises a first main cavity region wherein the materialto be heated is plad and a second coupling cavity located substantiallyat the rear of the enclosure. The microwave energy is inserted throughthe bottom wall of the enclosure into the rear coupling cavity. Thecoupling cavity is separated from the main cavity region by `a partitionwhich may be fabri cated partially from a metallic material andpartially from a dielectric material. The metallic portion of thepartition is located substantially adjacent the energy source to preventthe energy liront the source from immediately being directed toward and,thereby, overcoupling the load. The dielectric portion is locatedgenerally at a region above the material to be heated. The rear -cavityhas reflective surfaces that cause the energy to be deflected in ageneral upward direction where it is ultimately coupled from the rearcavity through the dielectric portion of the partition and, thence,downward over the load to be heated. A suitable stirring device may belocated in the coupling cavity so that the energy is uniformlydistributed throughout the main oven area. Such a configuration assuresa uniform distribution of energy throughout the load.

The invention may be more easily described with the help of theaccompanying drawings in which:

FIG. l -shows a sectional, elevation view of one embodiment of theinvention;

FIG. 2 shows a top sectional view of the embodiment of the inventionshown in FIG. 1 taken along the line 2-2 FIG. 3 shows a sectional,elevation view yof -a second embodiment of the invention; and

FIG. 4 shows ya top sectional view ot' the embodiment of the inventionshown in FIG. 3 taken .along the line 4 4.

In the apparatus shown in FIGS. 1 and 2 there is disclosed a microwaveheating apparatus 10 having a bottom section 11 and an upper section l2.Bottom sect-ion '1l houses power supplies, cooling devices, and otherelectrical or mechanical equipment that may be required for operation.Upper section 12 comprises a metallic enclosure into Ia portion of whichthe material to be heated is placed. The upper section 12 comprises aiirst oven cavity l5 'and a second coupling cavity 14 separated by apartition 16 having a metallic portion 17 and a dielectric portion 11S.Dielectric portion i8 is held at one end by a iirst bracket Sii attachedto the upper end of metallic portion i7 and at the other end by a secondbracket 31 attached at the front wall of upper section 12. At the frontor upper section 12 lthere is shown a door 13 s-lidably mounted toprovide an laccess opening for placing a material 19 to be heated inoven cavity 15 as shown. Material 1'9 is placed on a suitable dielectricplatform 20 he-ld within cavity i5 by mounting brackets 21. The door isarranged so that when it is closed it provides ,an adequate seal toprevent the escape of high frequency energy.

A microwave energy generator, such as a magnetron 22, is mounted at thebottom wall 23 of coupling cavity 14, the latter cavity Ibeing locatedin this embodiment lat the rear of enclosure 12. The magnetron may, forexample, have a dome-shaped portion 24 which functions as anelectromagnetic radiator of energy conducted thereto from the magnetroncavity resonator. Such magnetrons, as well as other types of magnetronswhich are also adaptable lfor use with apparatus 1li, are well known inthe art, tand, therefore, are not described in detail here. Other means,such as 'a waveguide, for coupling energy lthrough the bottom wall intothe enclosure, may also be used.

Coupling cavi-ty 14, into which the energy is inserted, has a 'cornerreflecting surface 26, placed substantially in the path of the enengyfrom source 22. Thus, the enorgy is directed generally into the upperregion 28` of enclosure 161. A mode stirring device -27 operated by amotor (not sho-wn) is mounted at the top wall of enclosure l0. Thus, theenergy which enters from microwave generating source 22 is coupledthrough the dielectric portion 13 of partition -16 downward toward thematerial 19 which is to be heated. The dielectric portion y18 provides ameans for preventing cooking igreases and vapors from entering couplingcavity 14 and spattering stirrer 27, magnetron 22 fand the reflectingwalls of cavity 14. It is within the scope of the invention to removethe dielect-ric portion 18` if cooking greases and vapors are not eX-pected to be a source of diiculty.

Coupling cavity i4 has dimensions which are relatively greater than thewave length of the high frequency energy source 22. The basic excitationfor the entering energy is the TMm mode but, because of the relativelylarge cavity size, substantially all modes are propagated withincoupling cavity 14. The structure of the invention allows optimumcoupling and stirring characteristics to be obtained. Thesecharacteristics may be determined by the stirrer position and the heightof metallic portion 17 of partition 16, the latter dimension being shownas the distance X in the ligure. By empirically adjusting dimension Xand the stirrer position, a satisfactory impedence match and energypattern can be obtained for a load placed within the main oven heatingcavity 15.

A second embodiment of the invention is shown in FIGS. 3 and 4 wherein amicrowave heating apparatus includes an oven enclosure 35 having a door36, said enclosure resting on a structure 37 housing electrical andmechanical equipment including a power supply for a magnetron energysource 3S mounted at the bottom wall 39 at the rear of oven enclosure35. The dome-shaped radiator 4t) of magnetron 38 is inserted into acoupling cavity 41 formed by a rst slanted partition 42 on one side, theslanted rear Wall 43 of enclosure 3S, and portions of the side, top andbottom walls o the enclosure. Partition 42 comprises a metallic portion44 having an opening 45 therein. Opening 45 is covered by a dielectricpiece 4.6 and a mode stirrer 47 is mounted at the rear wall 43 withincoupling cavity 41. A load 4g to be heated is placed within main ovenheating cavity 49. Material 48 may be mounted on a dielectric platform50 held by suitable brackets 51. For clarity the blades of mode stirrer47 are not shown in FIG. 4.

The configuration shown in FIGS. 3 and 4 thereby directs the energy fromsource 33 to load 48 through opening 45 so that the energy which isinserted at the bottom wall 39 of enclosure 35 is transmitted to theload from a point above the load to be heated. Thus, the configurationof FIGS. 3 and 4 provides the advantages of bottom-feed with theadvantages of coupling the bottom-fed energy to the load from a regionabove the load.

It is clear that other embodiments of the invention will occur to thoseskilled in the art that are within the scope of this invention. Forexample, the invention need not be limited to the use of a single energysource inasmuch as a plurality of magnetrons, or other high frequencysources, may be used to provide energy to the coupling cavity fortransmittal to the main oven cavity. Moreover, the coupling cavity neednot be located at the rear of the enclosure but may extend along theside walls, for example. Other suitable variations in the basicstructure of the invention may be devised by those in the art and,hence, the invention is not to be limited to the particular embodimentdisclosed herein except as defined by the appended claims.

What is claimed is:

1. A microwave heating apparatus comprising an enclosure having at leasta bottom wall and having a material-receiving cavity therein, an energycoupling cavity in the enclosure extending at one side and above thematerial-receiving cavity, a partition separating said cavities, meansfor generating and radiating microwave energy through the bottom wall ofsaid enclosure into said energy coupling cavity, said partition having adielectric portion located above said material-receiving cavity toprovide a transmission path for said microwave energy from said energycoupling cavity into said materialreceiving cavity whereby microwaveenergy is directed at material in said material-receiving cavity from alocation above said material.

2. A microwave heating apparatus comprising: substantially rectangularshaped enclosure having a bottom wall, a top wall and a front, baci; andtwo side walls, an L-shaped partition extending from said front wall tosaid bottom wall and dening a material-receiving cavity and an energycoupling cavity, an access door on said iront wall to provide access tosaid material-receiving cavity, means for generating and radiatingmicrowave energy through the bottom wall of said enclosure into saidenergy coupling cavity, said L-shaped partition having a dielectricportion located parallel to said bottom Wall to provide a transmissionpath for said microwave energy from said coupling cavity into saidmaterial-receiving cavity from a location above said material-receivingcavity, and stirrer means disposed in said energy coupling cavitydirectly above said dielectric portion for circulating said microwaveenergy in said energy coupling cavity down through said dielectricportion.

3. A microwave heating apparatus comprising: a substantially rectangularshaped enclosure having a bottom wall, a top wall and a front, back andtwo side walls, an L-shaped partition extending from said front wall tosaid bottom wall and deiining a material-receiving cavity and an energycoupling cavity, an access door on said front wall to provide access tosaid material-receiving cavity, means for generating and radiatingmicrowave energy through the bottom wall of said enclosure into saidenergy coupling cavity, said L-shaped partition having a dielectricportion located parallel to said bottom wall to provide a transmissionpath for said microwave energy from said coupling cavity into saidmaterialreceiving cavity from a location above said materialreceivingcavity, and stirrer means disposed in said energy coupling cavitydirectly above said dielectric portion for circulating said microwaveenergy in said energy coupling cavity down through said dielectricportion, and corner reflector means disposed in the corner formed by theintersection of said top wall and said back wall.

References Cited in the tile of this patent UNITED STATES PATENTS Longet al May 29, 1956 Smith Nov. 12, 1957 OTHER REFERENCES

1. A MICROWAVE HEATING APPARATUS COMPRISING AN ENCLOSURE HAVING AT LEASTA BOTTOM WALL AND HAVING A CAVMATERIAL-RECEIVING CAVITY THEREIN, ANENERGY COUPLING CAVITY IN THE ENCLOSURE EXTENDING AT ONE SIDE AND ABOVETHE MATERIAL-RECEIVING CAVITY, A PARTITION SEPARATING SAID CAVITIES,MEANS FOR GENERATING AND RADIATING MICROWAVE ENERGY THROUGH THE BOTTOMWALL OF SAID ENCLOSURE INTO SAID ENERGY COUPLING CAVITY, SAID PARTITIONHAVING A DIELECTRIC PORTION LOCATED ABOVE SAID MATERIAL-RECEIVING CAVITYTO PROVIDE A TRANSMISSION PATH FOR SAID MICROWAVE ENERGY FROM SAIDENERGY COUPLING CAVITY INTO SAID MATERIAL